The present application claims priority under 35 U.S.C. xc2xa7 119 of German Patent Application No. 100 51 802.2, filed on Oct. 18, 2000, the disclosure of which is expressly incorporated by reference herein in its entirety.
1. Field of the Invention
The present invention relates to a lamella of a headbox in, e.g., a paper, cardboard or tissue machine.
2. Discussion of Background Information
A lamella of a multi-layered headbox is known to the Applicant from European Patent Application No. EP 0 681 057 A2. In the nozzle of the disclosed headbox, at least one lamella is provided, which maintains the distance of two adjacent suspension flows down to a region of an exit nip. The lamella is formed of plastic with its modulus of elasticity preferably being smaller than about 80,000 N/mm2.
As is generally known, the plastic can be a polycarbonate (PC) which has been extremely successful as a material for many modern and technically demanding applications due to its specific characteristics. For example, the high-tech polycarbonate by the company Bayer AG with the trade name Makrolon(copyright), and that of General Electric with the trade name Lexan(copyright), have a global reputation.
The polycarbonate is used for inexpensive lamellae of applications in which the use of expensive lamellae is impossible or not suitable for economic reasons, e.g., in one-layered headboxes in which the lamellae end within the nozzle.
When polycarbonate is used as the material for lamellae, it is disadvantageous that the connection between the lamella and the headbox (or turbulence generator) must be constructed larger than sometimes desired due to the low stability of the polycarbonate. Additionally, polycarbonate has mechanical, chemical, thermal, and processing disadvantages as well.
Carbon fiber composite materials are better, yet also more expensive materials for lamellae, by which lamellae are produced in several components. The carbon fiber composite materials are particularly suitable in applications with very high requirements concerning shape stability and constancy of the crosswise thickness profile of the streams, in particular in multi-layered headboxes.
Until now, all materials known and used for lamellae for use in headboxes for producing a material web, such as a paper or cardboard web, by at least one fibrous stock suspension, have had in common the fact that they render the lamellae sensitive to the influence of mechanical forces, such as, e.g., during handling. Furthermore, they have a low resistance to high temperatures and alkaline solutions during cleaning of the headbox by xe2x80x9cboil out.xe2x80x9d Additionally, the service life of the lamellae is reduced due to the cited properties of the materials mentioned above.
Therefore, the present invention provides a headbox of the type generally discussed at the outset in which a lamella is provided with a better expense/effectiveness ratio for all possible utilizations and better withstands different operating conditions.
Accordingly, the present invention is directed to a headbox that includes a lamella constructed of at least one high-performance polymer, having high stability, high heat resistance, and good to very good resistance to alkaline solutions and/or acids.
High-performance polymers belong to the thermoplastic plastics, called xe2x80x9cthermoplastics,xe2x80x9d for short, and are characterized by a very high maximum operational temperature according to UL 746 B (U.S. testing regulations of the Underwriters"" Laboratories) and/or IEC 216, among other things, being in the range of about 160xc2x0 C. to about 260xc2x0 C., i.e., which exhibits a very good heat resistance, a good to very good resistance to alkaline solutions, and increased stability values.
Due to these characteristics (mechanic, thermal, and chemical), mentioned as examples, high-performance polymers are quite optimally suitable for use as the material for lamellae. They have an improved expense/effectiveness ratio and are able to withstand worsened operating conditions for longer.
In order to increase the mechanical characteristics of the lamella and to reduce its sensitivity to the influence of mechanical forces, the high-performance polymer has a tensile strength Rm (DIN 53455) in the range of about 50 N/mm2 to about 150 N/mm2, preferably about 70 N/mm2 to about 110 N/mm2, and a breaking elongation As (DIN 53455) in the range of about 20% to about 80%) preferably about 30% to about 60%. Furthermore, the high-performance polymer has a modulus of elasticity module E (DIN 53457, ISO 527-2) in the range of about 500 N/mm2 to about 10,000 N/mm2, preferably about 1,000 N/mm2 to about 5,000 N/mm2.
The connection between the lamella and the turbulence generator may be constructed in a smaller fashion, if the high-performance polymer has an impact strength when notched (ISO 179) of about 40 kJ/m2 to about 100 kJ/m2, preferably about 45 kJ/m2 to about 90 kJ/m2.
The behavior of the lamella concerning moisture and water (hydrolysis resistance) is decisively improved if the high-performance polymer has a moisture acceptance FA (ISO 62) in the range of about 0.05% to about 2%, preferably about 0.2% to about 12%.
In order to allow an efficient and inexpensive cleaning of a lamella, the high-performance polymer has a heat resistance WB (DIN 53461) in the range of about 120xc2x0 C. to about 230xc2x0 C., preferably about 170xc2x0 C. to about 220xc2x0 C., and a good to very good resistance to alkaline solutions. With these values, the performance of cleaning the headbox by xe2x80x9cboil outxe2x80x9d is possible, i.e., the presence of temperatures in the range of about 100xc2x0 C. and, simultaneously, the use of sodium hydroxide (NaOH) of about 20%.
In order to ensure the dimensional stability even during operation, the high-performance polymer has a low swelling Q, in particular, a low linear swelling QL, in the preferred range of about 0.02% to about 0.2%.
Out of the group of high-performance polymers that perform the above-mentioned requirements during operation and during cleaning of the headbox in an excellent fashion, polyphenylene sulphone (PPSU), polyether sulphone (PES), polyetherimide (PEI), and polysulphone (PSU) are recommended. The first three mentioned high-performance polymers, which were not developed until most recently, exhibit water absorption characteristics (DIN 53495) of 1.10% for PPSU; 2.00% for PES and 1.25% for PEI and heat resistance (DIN 53461) of 214xc2x0 C. for PPSU; 214xc2x0 C. for PES and 200xc2x0 C. for PEI, which are superior to those of PSU, i.e., 0.8% for DIN 53495 and 181xc2x0 C. for DIN 53461.
Depending on the use in question, the lamella reaching to the region of the nozzle may, on its structure less end region viewed in the flow direction, have a dull lamella end having a height less than about 0.4 mm, preferably less than about 0.3 mm, or have on its structured end region viewed in the flow direction, a dull lamella end having a height of more than about 0.5 mm. In another embodiment, a structured end region can be provided with a grooved structure having a rectangular and/or wedge-like and/or parabolic and/or round shape with a constant and/or varying depth.
In an advantageous embodiment, the lamella is completely constructed of one high-performance polymer in a homogenous design; in an alternative embodiment, the lamella end only is formed from at least one high-performance polymer. Thus, both embodiments ensure that at least the critical region of the lamella, i.e., the lamella end in the preferred embodiment of a lamella tip, has the advantageous characteristics of the high-performance polymer.
Furthermore, the lamella according to the invention may be embodied in a headbox with sectioned stock density control (dilution water technology). In this embodiment of the headbox, the possibility is created of allowing the sectional control of throughput, stock density, and, thus, basis weight and orientation of the fibers in the presence of the optimized lamellae.
In order to take into account present and future requirements of production with regard to the production amount, the headbox may be designed for a flow speed greater than about 1,500 m/s, preferably greater than about 1,800 m/s.
The lamella may also be integrated in a headbox embodied as a multi-layered headbox with the lamella essentially having the above-mentioned characteristics, embodied as a separating lamella of a multi-layered headbox.
It must be understood that the characteristics of the invention mentioned above and to be explained below can be used not only in the combinations mentioned, but also in different combinations or alone without departing from the scope of the invention.
The present invention is directed a lamella positionable in a headbox of a web production machine. The lamella is formed of at least one high-performance polymer; and the at least one high-performance polymer may include high stability, high heat resistance, and good to very good resistance to at least one of alkaline solution and acid.
In accordance with a feature of the present invention, the web production machine can include one of a paper, cardboard and tissue machine.
The high-performance polymer may have a tensile strength Rm (DIN 53455) in the range of about 50 N/mm2 to about 150 N/mm2, and a breaking elongation As (DIN 53455) in the range of about 20% to about 80%. The tensile strength Rm can be in a range of about 70 N/mm2 to about 110 N/mm2, and the breaking elongation As is in a range of about 30% to 60%.
The high-performance polymer can have a modulus of elasticity E (DIN 53457, ISO 527-2) in a range of about 500 N/mm2 to about 10,000 N/mm2. The modulus of elasticity E can be in a range of about 1,000 N/mm2 to about 5,000 N/mm2.
The high-performance polymer may have an impact strength when notched (ISO 179) of about 40 kJ/m2 to about 100 kJ/m2. The impact strength can be in a range of about 45 kJ/m2 to about 90 kJ/m2.
The high-performance polymer can have a moisture acceptance FA (ISO 62) in the range of about 0.05% to about 2%. The moisture acceptance FA may be in a range of about 0.2% to about 1.2%.
The high-performance polymer may have a heat resistance WB (DIN 53461) in the range of about 120xc2x0 C. to about 230xc2x0 C. The heat resistance WB can be in a range of about 170xc2x0 C. to about 220xc2x0 C.
The high-performance polymer may have a low swelling Q in a range of about 0.02% to about 0.2%. The low swelling Q can be a low linear swelling QL.
According to another feature of the invention, the high-performance polymer comprises at least one of polyphenylene sulphone (PPSU), polyether sulphone (PES), polyetherimide (PEI), and polysulphone (PSU).
Further, the headbox can include a nozzle, and the lamella may include a free end arranged to extend to a region of the nozzle. The free end may include an structure less end region with a dull lamella end having a height less than about 0.4 mm. The height of the dull lamella end can be less than about 0.3 mm.
According to still another feature of the present invention, the headbox can include a nozzle, and the lamella may include a free end arranged to extend to a region of the nozzle. The free end may include a structured end region with a dull lamella end having a height of more than about 0.5 mm. The structured end region can include grooves having at least one of (A) at least one of essentially rectangular, wedge-shaped, parabolic, and essentially round structure, and (B) varying depth. At least the lamella end can be constructed of the at least one high-performance polymer.
The lamella may be constructed of the high-performance polymer in a homogenous structure.
Further, the headbox may include a sectioned fiber suspension density control (dilution control).
According to another feature of the instant invention, the headbox can be designed for a flow speed greater than about 1,500 m/s, and preferably the flow speed may be greater than about 1,800 m/s.
Moreover, the lamella can be arranged as a separating lamella in a multi-layered headbox.
In accordance with still another feature of the invention, the lamella can be provided in combination with a headbox with a sectioned fiber suspension density control. The lamella may be located within the headbox.
Further, the lamella may be in combination with a headbox designed for a jet speed greater than about 1,500 m/s, and, preferably, the jet speed is greater than about 1,800 m/s.
In accordance with still yet another feature of the present invention, the lamella may be in combination with a multi-layered headbox. The lamella can be integrated into the multi-layered headbox as a separating lamella.
According to yet another feature of the instant invention, the web production machine can include one of a paper, cardboard, and tissue machine.
The present invention is directed to a headbox of a web production machine. The headbox includes a lamella formed of at least one high-performance polymer. The at least one high-performance polymer includes high stability, high heat resistance, and good to very good resistance to at least one of alkaline solution and acid
Other exemplary embodiments and advantages of the present invention may be ascertained by reviewing the present disclosure and the accompanying drawing.